When triggering a build, there should be a check whether the build is already running and if so, the new build should be queued and not run concurrently. If two builds are running concurrently, the second one always fails.
Comments from Openshift QE: This is more like a feature request. It is not enough to just check whether there is build running under project before a new build, should also check whether the running build is using the same resources with the new-started build, for if they are using different resources, there is no conflict to have two running build.
The second one fail usually because you can push same image to one registry (the second push will fail).
In the case where both builds are building against "HEAD" it's difficult to know if they are building the same thing (the commits might or might not be the same). we'd have to determine the commit to build before starting the build (which would also help with being able to rebuild an exact build).
trello'd: https://trello.com/c/Wz8FFwko/849-single-threaded-builds